I agree with what the position that the school has taken, even if it’s not the best for the child.
What will the school do if it comes out that one of the parents of another student are - say having an extramarital affair? Will they ask that child to leave as well?
Will the parents be having sex in front of the students? No, but the lesbians will be flaunting their “marriage” in front of the kids.
I’m sure the school recognizes that all have sinned and fall short, but allowing blatant sin to continue in unrepentant full display each day (homosexual relationships) in front of the children would be unacceptable.